The present invention relates to the art of measuring the moisture content of grains or like materials. More particularly, the present invention provides a direct reading moisture meter visually indicating the moisture content of a grain sample.
The moisture content of grains and like material has a direct consequence on the market value of grain, the ability to store the grain for prolonged periods, and the usability of the grain in processing and manufacturing apparatus. The moisture content in grain must, therefore, be monitored by the farmer, the elevator man, and the processor.
The most readily apparent indication of the importance of grain moisture content is the differential in price paid for grains of different moisture content. Grains with too high of a moisture content sell for a lower price than grains with a correct moisture content. Moreover, grains with lower moisture content than ideal lose weight with loss of moisture and, therefore, sell for a smaller amount than grains with an ideal moisture content.
Farmers dry grain to the preferred moisture content. Done properly, this maintains the grains food value, facilitate proper storage, and increase its value. Drying operations are energy intensive and, therefore, expensive. It is therefore advantageous to monitor the moisture content of the grain during drying and avoid over drying. This is best done with a portable moisture meter which allows testing to be done at the site of drying.
Portable grain moisture meters have been available in the past. One such device was described in U.S. Pat. No. 3,427,537. This device uses a resistance bridge network which compares the resistance of a grain sample of fixed volume placed between two electrodes to the resistance of a potentiometer. The user of the tester operated a dial mechanically connected to the potentiometer and watched for a null in a indicator light. The null indicated matched resistance between the sample and the adjusted potentiometer. At a null, the calibrated dial face of the potentiometer dial indicated the moisture content of the grain. This system requires the careful balancing of a resistance bridge network to obtain a correct reading. This is difficult because of the large voltage (80 volts) needed to operate the neon bulb null indicator. Moreover, the system requires the use of calibrated dial faces and complicated circuitry and a vibrator and transformer was used to produce the 600 volts of pulsed DC power required to operate the tester. These elements consume large amounts of current, requiring a large battery. The use of a mechanical vibrator, a transformer, and a heavy battery make for a very heavy unit.
Additional problems were also present in this device. The heart of the measuring apparatus was a resistance comparing bridge. Hard knocks and the like, often encountered on a farm could effect the precision and calibration of the bridge. Additionally, the front panel required a precision calibrated dial and lamp for nulling the bridge. These delicate components can easily be damaged or knocked out of calibration.
A later designed prior art device was essentially similar to the previously described device except that the mechanical vibrator was replaced with an electronic oscillator and the nulling lamp was replaced with an ammeter. This was a significant improvement as it removed a mechanical device subject to wear and malfunction and replaced it with a much longer lived electronic circuit. However, the need of a heavy transformer and battery remained. The use of an ammeter greatly improved the accuracy of the device by allowing a more precise nulling procedure. The use of a calibrated dial face with its attendant problems continued
An additional difficulty with both of the above devices was the requirement for the user to carefully monitor the temperature of the sample under test and apply a temperature compensation factor to arrive at a final value of moisture content.
The present invention contemplates a new and improved direct measuring grain moisture tester, which is much more reliable, rugged, lighter in weight, and requires less complicated activities of the operator than prior devices, thus overcoming all of the above referred to difficulties and others.